Generally, it is necessary to provide an infrared cut filter on an optical path in order to capture a color image using a camera (camera module) which includes a solid-state imaging device (image sensor). For example, Patent Literature (PTL) 1 discloses a camera module which includes a solid-state imaging device and an infrared cut filter. The reason for using an infrared cut filter is that a color filter conventionally used functions, in a visible light range, as a color filter which transmits only light of three primary colors, namely, blue, green, and red, but allows near-infrared light to pass through due to insufficient capability of blocking light in a near-infrared range, as shown in FIG. 2. Near-infrared light to which the human eye is not sensitive is sensed in a wavelength range up to 1100 nm on a silicon substrate used for a solid-state imaging device. Accordingly, without an infrared cut filter, near-infrared signals are mixed into red, green, and blue signals due to the influence of infrared light, resulting in a picture having an unnatural tone.
There is, however, a demand for obtaining a near-infrared image since near-infrared light includes a great amount of information. Examples of usages of a near-infrared image include monitoring and inspection of foodstuffs, agricultural products, chemicals, and paper money, for instance. Although an infrared-light-only solid-state imaging device is often used for such usages, there is a great demand for obtaining a near-infrared light image simultaneously with a visible light image. This is for achieving a reduction in the size and price of a device, and convenience of the device. In order to meet such a demand, in addition to conventional red, green, and blue pixels, a solid-state imaging device has been manufactured in which a near-infrared filter which transmits only near-infrared light (the filter may be referred to as a black filter due to blockage of light in a visible light range) is formed above light receiving portions. However, such a solid-state imaging device has a problem as already described that infrared light enters red, green, and blue pixels, which prevents obtaining a normal color image.
In order to solve this problem, a method for forming an infrared cut filter only above red, green, and blue pixels has been proposed. In PTL 2, a color filter made of an organic color material equivalent to that of a typical color filter is used, which is not specifically and clearly indicated as an infrared cut filter. In contrast, an interference filter made of an inorganic multilayer film is used as an infrared cut filter in PTLs 3 and 4. PTLs 2 and 3 fail to disclose in detail optical characteristics of an infrared filter and an infrared cut filter. PTL 4 does not require severe restrictions on optical characteristics of a filter, and clearly indicates that an infrared cut filter has a characteristic of blocking near-infrared light having a wavelength of about 600 nm to 800 nm or more, and an infrared transmission filter has a characteristic of transmitting near-infrared light having a wavelength of 750 nm or more.